High alpha linolenic acid flax (linseed) oil contains triglycerides which are composed of three unsaturated fatty acids side chains attached to a glycerol backbone. The three unsaturated fatty acids contain nonconjugated double bonds. Unsaturated indicates double bonds exist in the fatty acid chain and nonconjugated indicates these double bonds are separated by at least two single bonds. In High alpha linolenic acid flax (linseed) oil the three unsaturated fatty acid side chains consist primarily of alpha linolenic acid (C18: 3, omega 3, or 9,12,15-Octadecatrienoic acid), linoleic acid (C18: 2, or 9,12 Octadecadienoic acid) and oleic acid (C18: 1). High alpha linolenic acid flax (linseed) oil contains 65% or greater of alpha linolenic acid, an unsaturated fatty acid.
The linolenic content of non-High alpha linolenic acid Canadian flax cultivars varies from 49-62% depending on cultivar and growing conditions. Temperature during seed formation and photoperiod influences the concentration of fatty acid in the linseed oil. Cool temperatures and longer photoperiod increases linolenic content. Other factors which may affect the variability of linolenic content are soil moisture, soil fertility and presence of disease. It is noted that oil derived from most flax varieties has the following fatty acid composition:
Common NameFatty AcidPercentagePalmitic Acid16:0 4-10Palmitoleic Acid16:1<0.5Stearic Acid18:02-8Oleic Acid18:110-20Linoleic Acid18:214-20Alpha Linolenic Acid18:3 (n − 3)45-65Arachidic Acid20:0<0.5Eicosenoic Acid20.1<0.5
Linseed is grown primarily for its oil which has many industrial uses because of its drying property. Industrial uses of this oil include but are no means limited to the manufacture of paints and coatings, oil cloth, printing ink, soap, patent leather, core oils, brake linings, adhesives, manufacture of hardboard and fibreboard, protective coatings, paint primers, varnishes, lacquers, tarpaulin and other coated fabric, newsprint, caulking compounds, waterproofing compounds, mastic cements, shoe polish, herbicide and pesticide carrier, anti-spalling and curing agent for concrete surfaces including highways and bridges, tempering oil and bonding oil. Examples of industrial uses of linseed oil include but are no means limited to U.S. Pat. Nos. 5,965,633, 5,693,715, 5,653,789, 3,488,202 and 4,002,585.
In order for a naturally occurring oil to be classified as a “drying oil”, the drying index must exceed 70. A drying oil is defined as an oil which hardens to a tough, solid film with absorption of oxygen either from the environment (autoxidation) or with the addition of oxygen through chemical reactions i.e. with peracids. The term “drying” does not refer to the evaporation of water or other solvents, but to a series chemical reaction wherein the fatty acid side chains of the triglyceride are polymerized and cross linked. Drying oils are a key component of oil paint and many varnishes. Some commonly used drying oils include linseed oil, tung oil and perilla oil. The “drying”, hardening, or curing of linseed oil is the result of an exothermic reaction as the oil polymerizes to form long, chain-like molecules. The oil polymers cross-link to form a network which results in a solid film. Over time, ionic bonds also form between functional groups and metal ions of the pigment (for example in paints).
The drying index of an oil is calculated as % linoleic acid+2(% linolenic acid). The higher the drying index, the more quickly the oil will harden and the resultant film will be tougher and stronger. The drying index of High alpha linolenic acid flax (linseed) oil is 250 or greater. The excellent drying property of linseed oil arises from the ability to form cross-linkages by modifications of the nonconjugated double bonds in the fatty acid chain. Crosslinking occurs by several methods, primarily when the activated methylene groups in the unsaturated fatty acids or oils of the alkyd are oxidized to give hydroperoxides, which subsequently decompose to generate free radicals, leading to oxidative crosslinking. This oxidative crosslinking process is commonly accelerated by adding driers, such as, for example, the various salts of cobalt, zirconium, calcium, and manganese. Carbon to carbon cross linking can also occur. Cross-linking may be induced using chemicals i.e. peroxides, sulfur vulcanization, driers or by epoxidation or by physical means, i.e. light, heat, air, atmospheric oxygen, uv radiation or γ radiation, applying heat or blowing air while applying heat or by other methods. Using a drying oil with a high concentration of unsaturated fatty acid such as flax (linseed) oil yields a strong, tear-resistant film. For example, as compared to other drying oils, polymerized flax (linseed) oil used as a biodegradable coating for zein films, exhibits better resistance to water vapor permeability, toughness, and elongation without a decrease in tensile strength.
High alpha linolenic acid flax (linseed) oil contains a high concentration of unsaturated fatty acid thus yields more material available for cross linking and/or polymerization per unit weight. Thus materials based on a crosslinked oil result in a tougher, stronger final product.
Epoxidation of linseed oil is an effective method of inducing cross-linking and such films have high tensile strength, stiffness and tear resistance. Epoxidation replaces double bonds in the unsaturated fatty acid with a highly reactive cyclic ether or oxirane group. In this functional group there is an oxygen atom bonded to two neighboring carbon atoms creating a highly strained three sided ring. The high strain on the ring structure weakens the carbon-oxygen bonds allowing the ring to readily break open and form other, more stable bonds. The oxirane value of a compound is a measure of the number of epoxy groups present in the product i.e. a measure of the amount of epoxidized double bonds. Epoxidized High alpha linolenic acid flax (linseed) oil with 65% or greater alpha linolenic acid has an EO value or oxirane value of 10.0% or greater.